Assay for Tetrahymena telomerase activity. (a) In the assay, an oligonucleotide of the Tetrahymena telomere sequence is added to the extract, along with [32P]dGTP and unlabeled dTTP. Telomerase activity adds telomere repeats to the oligonucleotide. (b) Autoradiograph of a polyacrylamide gel analysis of reaction assays using different oligonucleotide sequences as substrate. The result shows that oligonucleotides of Tetrahymena and yeast telomere sequences are extended in six-